The present disclosure is directed to a connecting apparatus which secures a logging cable at its lower end through a cable head to a logging tool, and more particularly to one which provides for electrical feedthrough for the connecting conductors. It also serves as a bridle assembly which is electrically isolated. The context in which the present apparatus is used will be described below.
One logging technique involves suspending a logging tool constructed in a hermetically sealed sonde in a well borehole. In one approach, current is formed by the logging tool and flows out of the logging tool seeking a return point. The current will flow back to the logging tool at various places along the logging tool, cable head or the cable depending on the relative electrical isolation of the various components in the tool and the connective equipment. It is desirable to control the current return path so that it returns at a specified location. Otherwise, it might return at a point which is too close to the point of emission, or it may be forced to flow through excessive distances. Moreover, this current return path is partially dependent on the circumstances in which the tool is used, namely, the current return path may be shunted by well borehole fluids which are highly conductive in comparison with other pathways. With these circumstances in view, it is desirable to control that current return path. It has been determined that a return electrode can be spaced above the sonde by a specified distance which is approximately forty-six feet above the sonde so that the return electrode (a circular sleeve) is spaced a precise distance from the current emitting electrode in the sonde. Problems arise with this because it then defines an elongate tool assembly which is quite long. Sometimes, the sonde and the associated equipment assembled with it are so long that they are difficult to assemble at a drilling rig floor. Where there is an overhead draw works more than ninety feet above the rig floor, this does not pose much of a problem. However, it can be a problem where the drilling rig has been dismantled and moved away from the well. For instance, a small tilt up workover rig may be all that is available at a later time and they typically are constructed to extend only about thirty-three or thirty-four feet above the rig floor. In other words, there is not sufficient overhead room for extremely long tools to be positioned above the rig floor suspended from the overhead draw works.
The present apparatus sets out a rigid bridle assembly which positions the return electrode at the desired point. Moreover, the present disclosure sets out a bridle assembly which can be assembled from short segments so that any height of overhead draw works can be used, even the shortest derrick available. The bridle assembly of this disclosure further alternately includes an electrical isolation sub which is installed at one or more locations in the completed assembly wherein the sub has an open passageway through the middle for electrical connections to be positioned therein. This entails connection of one or more conductors from the cable head to the logging tool proper. It is not uncommon to construct logging cables with multiple conductors, typically even as many as seven. The logging cable thus normally terminates at a cable head, and the present apparatus defines a short connective sub which permits those conductors to be extended therethrough. Indeed, while the cable head may bring in only seven conductors, there may be other conductors, for instance those which connect with the return electrode, and to this end, the present system is connected so that it supports a specified large number of internal conductors. In the preferred embodiment, as will be disclosed, this provides plug and socket assemblies which have nineteen pins in one embodiment.
The present apparatus further includes sufficient structure to be rigid and thus obtain the benefit of metal construction, but the surface is nevertheless isolated so that it does not serve as a current return electrode. To the extent that there are metal components exposed on the exterior, they are isolated. Moreover, the bulk of the exterior is wrapped in or covered with an insulative material.
With the foregoing background in view, the present apparatus is described as an elongate repetitively installed pin and box connected subassembly which threads together to form a completed assembly. An alternate device is a relatively short isolation sub. In the preferred embodiment, the short isolation sub is constructed of upper and lower sleeves having appropriate threads for assembly in a tool, and the sleeves are coupled together in a non-rotating fashion. In the completed assembly, there is an axial passage therethrough for electrical conductors. In addition to the short isolation sub, there is the isolator joint which is substantially longer. It has the benefit of a steel internal sub for strength and reinforcing, but nevertheless it also includes an external wrap. This is included for assembly purposes yet also provides electrical insulation around the structure. The isolator joint has appropriate threaded connections at both ends and appropriately positioned multiple pin plugs and sockets so that electrical current is conducted through the center of this axially hollow structure by means of multiple conductors. Ideally, three of the isolator joints are assembled to position a return electrode at a desired spacing from a current emitting electrode on a sonde supported by the present apparatus which is installed between the sonde and the lower end of a logging cable. An isolator joint is also placed above the return electrode to isolate it from the cable head.